What does «agua dura» mean in Spanish?
- When water contains certain dissolved mineral matter, which reacts with soap, giving insoluble clots, it is said to be hard water. In limestone soils, the dissolving action of groundwater loaded with carbon dioxide converts calcium carbonate into soluble calcium bicarbonate, which is responsible for the temporary hardness of the water: CaCO3 + H20 + CO2 -> Ca(HC03)2 In dolomitic soils, magnesium bicarbonate, Mg(HCO3)2, is formed in the same way. The hardness of some natural waters is due to the presence of ferrous bicarbonate, Fe(HCO3)2. When the water is boiled, the bicarbonates are transformed into insoluble carbonates that precipitate, thus eliminating the temporary hardness. The presence of dissolved calcium or magnesium sulfates in the water causes permanent hardness.